1. Field of the Invention
This invention relates to biological methods and products useful in agriculture. More specifically, the present invention is directed to a method for controlling fungal diseases in plants.
2. Description of the Prior Art
Fungal diseases cause great economic damage to agricultural and ornamental crops around the world. Currently, most of the pesticides in use for control of fungal diseases are synthetic compounds. Many of these chemical fungicides are classified as carcinogens by the EPA, and are toxic to humans, wildlife, and other non-target species. In addition, many reports indicate that chemical fungicides have become less effective due to the development of pathogen resistance. (Schwinn et al. 1991, Advances in plant pathology: Phytophthora infestans, the cause of late blight of potato, Academic Press, San Diego; Jones and Ehret, 1976, Plant Dis. Rep. 60:765-769; Ferrin, 1992, Plant Disease, 76:60-63, p. 82-84). Alarm resulting from the growing incidence of pesticide resistance has prompted global efforts directed toward the search for alternative pest control strategies. One such strategy is biological control with antagonistic microorganisms or microbial products to directly or indirectly control target pests. See, for example, Stanghellini et al. 1998, U.S. Pat. No. 5,767,090. Biological control can be safer for humans and the environment, and less expensive to develop than chemical pesticides.
Screening programs have identified certain bacterial strains that exhibit antifungal activities. (Stabb et al. 1990, Applied Environ. Microbiol. 60(12):4404-4412; Broadbent et al. 1971, Austral. J Biol. Sci. 24:925-944; Baker et al. 1982, Biological control of plant pathogens, American Phytopathological Society, St. Paul, Minn., 433 pp). One of the mechanisms of bacterial antagonism to fungi is antibiosis, which consists in the inhibition or destruction of one organism by a metabolic product of another. Antibiosis can occur by at least three distinct mechanisms. First, it can occur by way of hydrolytic cell wall-degrading enzymes such as xylanases, mannanases, cellulases, proteases, and chitinases. Second, it can manifest as an enzyme that decreases fungal osmotolerance such as trehalase. Third, it can occur by the administration and activity of antibiotics.
The term antibiotic is very broad and includes widely disparate mechanisms. For example, penicillin interferes with cell wall formation, streptomycin interferes with protein synthesis; and siderophores are compounds that inhibit growth by sequestering needed iron. By 1977, production of at least 66 different antibiotics had been reported in different strains of Bacillus (Katz and Demain, 1977, Bacteriol. Rev. 41:449-474). Furthermore, some strains of Bacillus cereus and B. thuringiensis have the ability to produce auxiliary proteins; compounds that enhance the activity of bacterial pesticides. (Warren et al. 1998, U.S. Pat. No. 5,770,696).
Several strains of Bacillus cereus have been patented for their antifungal properties against plant pathogens (Handelsman et al. 1996, U.S. Pat. No. 5,552,138; Handelsman et al. 1997, U.S. Pat. No. 5,700,462; Handelsman et al. 2000, U.S. Pat. No. 6,034,124). The antibiotics zwittermicin and kanosamine are commonly produced by strains of Bacillus cereus (Handelsman, supra). Production of the antibiotic iturin A by a strain of Bacillus amyloliquefaciens was demonstrated for control of fungi that cause disease in animals (Tanaka et al. 1995, U.S. Pat. No. 5,470,827), but it is not known to use Bacillus amyloliquefaciens for control of fungi in agriculture. An abundant amount of research has been published on the fungal biocontrol activity of diverse strains of Bacillus subtilis, and their diverse antifungal antibiotics (Asaka and Shoda, 1996, Appl. Env. Microbiol. 62(11):4081-4085; Guelder et al. 1988, J. Agric. Food Chem. 36:366-370; Mckeen et al. 1986, Phytopathology 76(2):136-139). Fungal biocontrol efficiency varies widely among strains of Bacillus subtilis as demonstrated in a study where twenty-one strains of Bacillus subtilis were evaluated simultaneously against fourteen fungal pathogens (Utkhede and Sholberg, 1986, Can. J Microbiol. 32:963-967). Various strains of Bacillus subtilis with antifungal activity have been patented (Pusey and Wilson, 1988, U.S. Pat. No. 4,764,371; Bacon and Hinton, 1999, U.S. Pat. No. 5,994,117; Heins et al., 2000, U.S. Pat. No. 6,103,228).
While various biocontrol agents for control of pathogenic fungi are known in the art, available biocontrol products cover a small range of crops and have a very small share of the crop protection market. (Whipps, 1994, Advances in biological control in protected crops, Brighton Crop Prot. Conf. Pest Dis. 9B:1259-1264). Present fungal biocontrols are not perceived as effective, reliable, and cost-efficient for present large-scale agricultural use. Poor activity has been linked to poor colonization due to competition by microorganism, or release of plant exudates which selectively encourage or prevent colonization by specific groups of microorganisms (Berger et al. 1996, Phytopathology 86(5):428-433). In contrast to fungicides, biocontrol agents often lack activity at higher pathogen concentrations (Whipps, supra). The approach taken by most researchers is the use of a characterized single strain biocontrol agent. One drawback to the single strain biocontrol approach is that environmental conditions in agriculture fields are highly dynamic and therefore not always optimal for a single biocontrol strain. So it can be difficult or impossible for this single strain to colonize the foliage, roots and soil around the roots, and maintain populations at levels high enough to suppress the growth of fungal pathogens during the whole crop cycle. On the other side of the spectrum of biological diversity, uncharacterized multi-species biocontrol products such as compost teas have proven unreliable, probably because of uncontrollable changes in the species composition of the microbial community. A biocontrol approach, however, using a combination of strains with antifungal activities can be more effective than a single strain biocontrol agent as there are more chances of successful colonization and more antifungal mechanisms operating simultaneously. A few products that include different bacteria strains for biocontrol of fungal diseases in plants have been patented (Cuero et al., 1998, U.S. Pat. No. 5,830,459; Drahos and Miller, 2001, U.S. Pat. No. 6,194,193; Ocamb et al., 2000, U.S. Pat. No. 6,133,196). There exists a continuing need for alternative biocontrol compositions and methods.
All documents or publications cited herein are incorporated by reference in their entirety, to the extent not inconsistent with the explicit teachings set forth herein.
This invention relates to a novel approach to reduce or suppress the incidence or severity of fungal-induced diseases in plants, which, in a preferred embodiment, consists of a synergistic combination of novel Bacillus strains (Bacillus cereus xe2x80x9cB1,xe2x80x9d Bacillus amyloliquefaciens xe2x80x9cB2,xe2x80x9d Bacillus cereus xe2x80x9cB3,xe2x80x9d and Bacillus subtilis xe2x80x9cB4xe2x80x9d) that inhibits the growth of fungal pathogens. To this end, the biocontrol activity of the blend is more consistent, and provides biocontrol over a wider range of fungal pathogens, than that obtained by the individual components of the blend, which themselves are novel and can be used as biocontrol agents.
In a preferred embodiment, the treatment composition of the present invention consists of a unique combination of bacteria, specifically strains Bacillus cereus xe2x80x9cB 1,xe2x80x9d Bacillus amyloliquefaciens xe2x80x9cB2,xe2x80x9d Bacillus cereus xe2x80x9cB3,xe2x80x9d and Bacillus subtilis xe2x80x9cB4.xe2x80x9d
Accordingly, it is an object of the present invention to provide evidence of suppression of fungal diseases by a biocontrol product on different food crop plants.
Further objects and advantages of the present invention will become apparent by reference to the following detailed disclosure of the invention and appended photographs.
Bacillus cereus xe2x80x9cB1,xe2x80x9d Bacillus amyloliquefaciens xe2x80x9cB2,xe2x80x9d Bacillus cereus xe2x80x9cB3,xe2x80x9d and Bacillus subtilis xe2x80x9cB4xe2x80x9d have been deposited under the provisions of the Budapest Treaty with the Agriculture Research Culture Collection (NRRL) having a place of business at 1815 N. University Street, Peoria, Ill. 61604, U.S.A. The accession numbers at NRRL are: Bacillus cereus xe2x80x9cB1xe2x80x9d (NRRL B-30517), Bacillus amyloliquefaciens xe2x80x9cB2xe2x80x9d (NRRL B-30518), Bacillus cereus xe2x80x9cB3xe2x80x9d (NRRL B-30519), and Bacillus subtilis xe2x80x9cB4xe2x80x9d (NRRL B-30520).